Photocatalytic degradation of pesticide methomyl: determination of the reaction pathway and identification of intermediate products

In a chemical system with many chemical species several questions can be asked: what species react with other species: in what temporal order: and with what results? These questions have been asked for over one hundred years about simple and complex chemical systems, and the answers constitute the macroscopic reaction mechanism. In Determination of Complex Reaction Mechanisms authors John Ross, Igor Schreiber, and Marcel Vlad present several systematic approaches for obtaining information on the causal connectivity of chemical species, on correlations of chemical species, on the reaction pathway, and on the reaction mechanism. Basic pulse theory is demonstrated and tested in an experiment on glycolysis. In a second approach, measurements on time series of concentrations are used to construct correlation functions and a theory is developed which shows that from these functions information may be inferred on the reaction pathway, the reaction mechanism, and the centers of control in that mechanism. A third approach is based on application of genetic algorithm methods to the study of the evolutionary development of a reaction mechanism, to the attainment given goals in a mechanism, and to the determination of a reaction mechanism and rate coefficients by comparison with experiment. Responses of non-linear systems to pulses or other perturbations are analyzed, and mechanisms of oscillatory reactions are presented in detail. The concluding chapters give an introduction to bioinformatics and statistical methods for determining reaction mechanisms.

Download Full-text

Spectrophotometric determination of nicradipine and isradipine in pharmaceutical formulations

Chemical Industry and Chemical Engineering Quarterly ◽

10.2298/ciceq0902069a ◽

2009 ◽

Vol 15 (2) ◽

pp. 69-76 ◽

Cited By ~ 1

Author(s):

S.M. Al-Ghannam ◽

A.M. Al-Olyan

Keyword(s):

Standard Deviation ◽

Detection Limit ◽

Reaction Pathway ◽

Pharmaceutical Preparations ◽

Pharmaceutical Formulations ◽

Molar Absorptivity ◽

Zinc Powder ◽

Conditional Stability ◽

Conditional Stability Constant

A sensitive spectrophotometric method was developed for the determination of some 1,4-dihydropyridine compounds namely, nicardipine and isradipine either in pure form or in pharmaceutical preparations. The method is based on the reduction of nicardipine and isradipine with zinc powder and calcium chloride followed by further reduction with sodium pentacyanoaminoferrate (II) to give violet and red products having the absorbance maximum at 546 and 539 nm with nicardipine and isradipine, respectively. Beer's law was obeyed over the concentration range 8.0-180 ?g/ml with the detection limit of 1.67 ?g/ml for nicardipine and 8.0-110 ?g/ml with the detection limit of 1.748 ?g/ml for isradipine. The analytical parameters and their effects on the reported methods were investigated. The molar absorptivity, quantization limit, standard deviation of intercept (Sa), standard deviation of slope (Sb) and standard deviation of the residuals (Sy/x) were calculated. The composition of the result compounds were found 1:1 for nicardipine and 1:2 for isradipine by Job's method and the conditional stability constant (Kf) and the free energy changes (?G) were calculated for compounds formed. The proposed method was applied successfully for the determination of nicardipine and isradipine in their dosage forms. The results obtained were in good agreement with those obtained using the reference or official methods. A proposal of the reaction pathway was presented.

Download Full-text

Thermodynamics of primary antioxidant action of flavonols in polar solvents

Acta Chimica Slovaca ◽

10.2478/acs-2019-0016 ◽

2019 ◽

Vol 12 (1) ◽

pp. 108-118 ◽

Cited By ~ 2

Author(s):

Martin Michalík ◽

Ján Rimarčík ◽

Vladimír Lukeš ◽

Erik Klein

Keyword(s):

Reaction Pathway ◽

Hydrogen Atom Transfer ◽

Antioxidant Effect ◽

Antioxidant Action ◽

Polar Solvents ◽

Polar Media ◽

Primary Antioxidant ◽

Intramolecular Hydrogen

Abstract Very recently, a report on the antioxidant activity of flavonoids has appeared, where authors concluded that Hydrogen Atom Transfer mechanism represents the thermodynamically preferred mechanism in polar media (https://doi.org/10.1016/j.foodres.2018.11.018). Unfortunately, serious errors in the theoretical part of the paper led to incorrect conclusions. For six flavonols (galangin, kaempferol, quercetin, morin, myricetin, and fisetin), reaction enthalpies related to three mechanisms of the primary antioxidant action were computed. Based on the obtained results, the role of intramolecular hydrogen bonds (IHB) in the thermodynamics of the antioxidant effect is presented. Calculations and the role of solvation enthalpies of proton and electron in the determination of thermodynamically preferred mechanism is also briefly explained and discussed. The obtained results are in accordance with published works considering the Sequential Proton-Loss Electron-Transfer thermodynamically preferred reaction pathway.

Download Full-text

Spectrofluorometric determination of nicardipine, nifedipine and isradipine in pharmaceutical preparations and biological fluids

Open Chemistry ◽

10.2478/s11532-008-0011-x ◽

2008 ◽

Vol 6 (2) ◽

pp. 222-228 ◽

Cited By ~ 10

Author(s):

Sheikha Al-Ghannam ◽

Abeer Al-Olyan

Keyword(s):

Fluorescence Intensity ◽

Reaction Pathway ◽

Biological Fluids ◽

Sodium Dodecyl ◽

Pharmaceutical Preparations ◽

Reduction Reaction ◽

Factors Affecting ◽

Plasma And Urine Samples

AbstractA simple and highly sensitive spectrofluorometric method was developed for the determination of some 1,4-dihydropyridine compounds namely, nicardipine, nifedipine and isradipine in pharmaceutical preparations and biological fluids. The method is based on the reduction of nicardipine, nifedipine and isradipine with Zn/HCl and measuring the fluorescence intensity obtained (λem/λex) at 460/364, 450/393 and 446/360 nm, respectively. The factors affecting the development of the fluorophore and its stability were studied and optimized. The effect of some surfactants such as β-cyclodextrin (βCD), carboxymethylcelullose (CMC), sodium dodecyl sulphate (SDS) and triton X-100, on the fluorescence intensity was studied. The fluorescence intensity-concentration plots of nicardipine, nifedipine and isradipine were rectilinear over the ranges 0.4–6.0, 0.2–4.0 and 0.1–9.0 μg ml−1 with detection limits of 0.0028, 0.017 and 0.016 μg ml−1, respectively. The proposed method was successfully applied to commercial tablets containing the compounds; the percentage recovery agreed well with those obtained using the official methods. The method was further extended to the in vitro determination of the compounds in spiked human plasma and urine samples. A proposal of the reduction reaction pathway was postulated.

Download Full-text

Spectrofluorimetric Determination of Vigabatrin and Gabapentin in Dosage Forms and Spiked Plasma Samples Through Derivatization with 4-Chloro-7-Nitrobenzo-2-Oxa-1,3-Diazole

Journal of AOAC International ◽

10.1093/jaoac/84.4.1017 ◽

2001 ◽

Vol 84 (4) ◽

pp. 1017-1024 ◽

Cited By ~ 17

Author(s):

Ekram M Hassan ◽

Fathalla Belal ◽

Omar A Al-Deeb ◽

Nasr Y Khalil

Keyword(s):

Reaction Pathway ◽

Dosage Forms ◽

Specific Method ◽

Plasma Samples ◽

Spiked Plasma ◽

Highly Sensitive ◽

Percent Recovery ◽

Spectrofluorimetric Determination ◽

Label Claim

Abstract A highly sensitive and specific method is proposed for the determination of vigabatrin (I) and gabapentin (II) in their dosage forms and spiked human plasma. The method is based on coupling the drugs with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole in borate buffer at pH 7.1 and measuring the resulting fluorescence at 532 nm after excitation at 465 nm. The fluorescence intensity was a linear function of the concentration of the drugs over the ranges of 1.3–6.5 and 1.7–8.5 μg/mL for I and II, respectively. Minimum detectability values were 0.54 μg/mL (4.2 × 10−6M) and 0.97 μg/mL (5.7 × 10−6M) for I and II, respectively, under the described conditions. The proposed method was successfully applied to the determination of the 2 drugs in their dosage forms, and the percent recoveries ± standard deviation (SD) were 104.53 ± 1.2 and 100.00 ± 1.32 of the label claim for I and II, respectively. The method was further applied to the determination of vigabatrin in spiked plasma samples. The percent recovery ± SD was 101.58 ± 2.68. Interference from endogenous α-amino acids was overcome through selective complexation with freshly prepared Cu(OH)2. The interference likely to be encountered from co-administered drugs, such as carbamazepine, cimetidine, clonazepam, clopazam, phenobarbital, valproic acid, and lamotrigine, was also studied. A reaction pathway is suggested.

Download Full-text

Electrochemical Microreactor for the Determination of Intermediate Products in Fuel Cell Reactions

ECS Meeting Abstracts ◽

10.1149/ma2009-02/10/890 ◽

2009 ◽

Keyword(s):

Fuel Cell ◽

Intermediate Products ◽

Electrochemical Microreactor

Download Full-text

Rational Design and Testing of Anti-Knock Additives

Energies ◽

10.3390/en13184923 ◽

2020 ◽

Vol 13 (18) ◽

pp. 4923

Author(s):

Andrew D. Ure ◽

Manik K. Ghosh ◽

Maria Rappo ◽

Roland Dauphin ◽

Stephen Dooley

Keyword(s):

Rational Design ◽

Reaction Pathway ◽

Cetane Number ◽

Research Octane Number ◽

Ignition Quality ◽

Ignition Quality Tester ◽

Generic Design ◽

The Relationship ◽

Design And Testing

An innovative and informed methodology for the rational design and testing of anti-knock additives is reported. Interaction of the additives with OH● and HO2● is identified as the key reaction pathway by which non-metallic anti-knock additives are proposed to operate. Based on this mechanism, a set of generic design criteria for anti-knock additives is outlined. It is suggested that these additives should contain a weak X-H bond and form stable radical species after hydrogen atom abstraction. A set of molecular structural, thermodynamic, and kinetic quantities that pertain to the propensity of the additive to inhibit knock by this mechanism are identified and determined for a set of 12 phenolic model compounds. The series of structural analogues was carefully selected such that the physical thermodynamic and kinetic quantities could be systematically varied. The efficacy of these molecules as anti-knock additives was demonstrated through the determination of the research octane number (RON) and the derived cetane number(DCN), measured using an ignition quality tester (IQT), of a RON 95 gasoline treated with 1 mole % of the additive. The use of the IQT allows the anti-knock properties of potential additives to be studied on one tenth of the scale, compared to the analogous RON measurement. Using multiple linear regression, the relationship between DCN/RON and the theoretically determined quantities is studied. The overall methodology reported is proposed as an informed alternative to the non-directed experimental screening approach typically adopted in the development of fuel additives.

Download Full-text